.\" -*- nroff -*-
.\" Copyright 2013 Los Alamos National Security, LLC. All rights reserved.
.\" Copyright (c) 2010-2015 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" $COPYRIGHT$
.TH MPI_Comm_split_type 3 "Jun 10, 2020" "4.0.4" "Open MPI"
.SH NAME
\fBMPI_Comm_split_type \fP \- Creates new communicators based on colors and keys.

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Comm_split_type(MPI_Comm \fIcomm\fP, int\fI split_type\fP, int\fI key\fP,
	MPI_Info info, MPI_Comm *\fInewcomm\fP)

.fi
.SH INPUT PARAMETERS
.ft R
.TP 1i
comm
Communicator (handle).
.TP 1i
split_type
Type of processes to be grouped together (integer).
.TP 1i
key
Control of rank assignment (integer).
.TP 1i
info
Info argument (handle).

.SH OUTPUT PARAMETERS
.ft R
.TP 1i
newcomm
New communicator (handle).
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
This function partitions the group associated with \fIcomm\fP into disjoint subgroups, based on
the type specied by \fIsplit_type\fP. Each subgroup contains all processes of the same type.
Within each subgroup, the processes are ranked in the order defined by the value of the
argument \fIkey\fP, with ties broken according to their rank in the old group. A new communicator
is created for each subgroup and returned in newcomm. This is a collective call;
all processes must provide the same \fIsplit_type\fP, but each process is permitted to provide
different values for key. An exception to this rule is that a process may supply the type
value MPI_UNDEFINED, in which case newcomm returns MPI_COMM_NULL.

.SH SPLIT TYPES
.ft R
.TP 1i
MPI_COMM_TYPE_SHARED
This type splits the communicator into subcommunicators, each of which can create a shared memory region.

.ft R
.TP 1i
OMPI_COMM_TYPE_NODE
Synonym for MPI_COMM_TYPE_SHARED.
.ft R
.TP 1i
OMPI_COMM_TYPE_HWTHREAD
This type splits the communicator into subcommunicators, each of which belongs to the same hardware thread.
.ft R
.TP 1i
OMPI_COMM_TYPE_CORE
This type splits the communicator into subcommunicators, each of which belongs to the same core/processing unit.
.ft R
.TP 1i
OMPI_COMM_TYPE_L1CACHE
This type splits the communicator into subcommunicators, each of which belongs to the same L1 cache.
.ft R
.TP 1i
OMPI_COMM_TYPE_L2CACHE
This type splits the communicator into subcommunicators, each of which belongs to the same L2 cache.
.ft R
.TP 1i
OMPI_COMM_TYPE_L3CACHE
This type splits the communicator into subcommunicators, each of which belongs to the same L3 cache.
.ft R
.TP 1i
OMPI_COMM_TYPE_SOCKET
This type splits the communicator into subcommunicators, each of which belongs to the same socket.
.ft R
.TP 1i
OMPI_COMM_TYPE_NUMA
This type splits the communicator into subcommunicators, each of which belongs to the same NUMA-node.
.ft R
.TP 1i
OMPI_COMM_TYPE_BOARD
This type splits the communicator into subcommunicators, each of which belongs to the same board.
.ft R
.TP 1i
OMPI_COMM_TYPE_HOST
This type splits the communicator into subcommunicators, each of which belongs to the same host.
.ft R
.TP 1i
OMPI_COMM_TYPE_CU
This type splits the communicator into subcommunicators, each of which belongs to the same computational unit.
.ft R
.TP 1i
OMPI_COMM_TYPE_CLUSTER
This type splits the communicator into subcommunicators, each of which belongs to the same cluster.

.SH NOTES
.sp
The communicator keys denoted with an
.I OMPI_
prefix instead of an
.I MPI_
prefix are specific to Open MPI, and are not part of the MPI
standard.  Their use should be protected by the
.I OPEN_MPI
C preprocessor macro.

.SH ERRORS
Almost all MPI routines return an error value; C routines as the value
of the function and Fortran routines in the last argument.
.sp
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for
I/O function errors. The error handler may be changed with
MPI_Comm_set_errhandler; the predefined error handler
MPI_ERRORS_RETURN may be used to cause error values to be
returned. Note that MPI does not guarantee that an MPI program can
continue past an error.

.SH SEE ALSO
.ft R
.sp
MPI_Comm_create
.br
MPI_Intercomm_create
.br
MPI_Comm_dup
.br
MPI_Comm_free
.br
MPI_Comm_split

